21st century ocean forcing of the Greenland Ice Sheet for modeling of sea level contribution

Abstract. Changes in the ocean are expected to be an important determinant of the Greenland Ice Sheet's future sea level contribution. Yet representing these changes in continental-scale ice sheet models remains challenging due to the small scale of the key physics, and limitations in processing understanding. Here we present the ocean forcing strategy for Greenland Ice Sheet models taking part in the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), the primary community effort to provide 21st century sea level projections for the Intergovernmental Panel on Climate Change 6th Assessment Report. Beginning from global atmosphere-ocean general circulation models, we describe two complementary approaches to provide ocean boundary conditions for Greenland Ice Sheet models, termed the retreat and submarine melt implementations. The retreat implementation parameterizes glacier retreat as a function of projected submarine melting, is designed to be implementable by all ice sheet models, and results in retreat of around 1 and 15 km by 2100 in RCP2.6 and 8.5 scenarios respectively. The submarine melt implementation provides estimated submarine melting only, leaving the ice sheet model to solve for the resulting calving and glacier retreat, and suggests submarine melt rates will change little under RCP2.6 but will approximately triple by 2100 under RCP8.5. Both implementations have necessarily made use of simplifying assumptions and poorly-constrained parameterisations and as such, further research on submarine melting, calving and fjord-shelf exchange should remain a priority. Nevertheless, the presented framework will allow an ensemble of Greenland Ice Sheet models to be systematically and consistently forced by the ocean for the first time, and should therefore result in a significant improvement in projections of the Greenland ice sheet's contribution to future sea level change.

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Twenty-first century ocean forcing of the Greenland ice sheet for modelling of sea level contribution

The Cryosphere ◽

10.5194/tc-14-985-2020 ◽

2020 ◽

Vol 14 (3) ◽

pp. 985-1008 ◽

Cited By ~ 7

Author(s):

Donald A. Slater ◽

Denis Felikson ◽

Fiamma Straneo ◽

Heiko Goelzer ◽

Christopher M. Little ◽

...

Keyword(s):

Sea Level ◽

General Circulation ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

General Circulation Models ◽

Glacier Retreat ◽

Small Scale ◽

Intergovernmental Panel ◽

Continental Scale ◽

The Impact

Abstract. Changes in ocean temperature and salinity are expected to be an important determinant of the Greenland ice sheet's future sea level contribution. Yet, simulating the impact of these changes in continental-scale ice sheet models remains challenging due to the small scale of key physics, such as fjord circulation and plume dynamics, and poor understanding of critical processes, such as calving and submarine melting. Here we present the ocean forcing strategy for Greenland ice sheet models taking part in the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), the primary community effort to provide 21st century sea level projections for the Intergovernmental Panel on Climate Change Sixth Assessment Report. Beginning from global atmosphere–ocean general circulation models, we describe two complementary approaches to provide ocean boundary conditions for Greenland ice sheet models, termed the “retreat” and “submarine melt” implementations. The retreat implementation parameterises glacier retreat as a function of projected subglacial discharge and ocean thermal forcing, is designed to be implementable by all ice sheet models and results in retreat of around 1 and 15 km by 2100 in RCP2.6 and 8.5 scenarios, respectively. The submarine melt implementation provides estimated submarine melting only, leaving the ice sheet model to solve for the resulting calving and glacier retreat and suggests submarine melt rates will change little under RCP2.6 but will approximately triple by 2100 under RCP8.5. Both implementations have necessarily made use of simplifying assumptions and poorly constrained parameterisations and, as such, further research on submarine melting, calving and fjord–shelf exchange should remain a priority. Nevertheless, the presented framework will allow an ensemble of Greenland ice sheet models to be systematically and consistently forced by the ocean for the first time and should result in a significant improvement in projections of the Greenland ice sheet's contribution to future sea level change.

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Estimation of the Greenland ice sheet surface mass balance for the 20th and 21st centuries

The Cryosphere ◽

10.5194/tc-2-117-2008 ◽

2008 ◽

Vol 2 (2) ◽

pp. 117-129 ◽

Cited By ~ 68

Author(s):

X. Fettweis ◽

E. Hanna ◽

H. Gallée ◽

P. Huybrechts ◽

M. Erpicum

Keyword(s):

Mass Balance ◽

Multiple Regression ◽

21St Century ◽

General Circulation ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

General Circulation Models ◽

Climate Simulation ◽

Surface Mass Balance ◽

Surface Mass

Abstract. Results from a regional climate simulation (1970–2006) over the Greenland ice sheet (GrIS) reveals that more than 97% of the interannual variability of the modelled Surface Mass Balance (SMB) can be explained by the GrIS summer temperature anomaly and the GrIS annual precipitation anomaly. This multiple regression is then used to empirically estimate the GrIS SMB since 1900 from climatological time series. The projected SMB changes in the 21st century are investigated with the set of simulations performed with atmosphere-ocean general circulation models (AOGCMs) of the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4). These estimates show that the high surface mass loss rates of recent years are not unprecedented in the GrIS history of the last hundred years. The minimum SMB rate seems to have occurred earlier in the 1930s and corresponds to a zero SMB rate. The AOGCMs project that the SMB rate of the 1930s would be common at the end of 2100. The temperature would be higher than in the 1930s but the increase of accumulation in the 21st century would partly offset the acceleration of surface melt due to the temperature increase. However, these assumptions are based on an empirical multiple regression only validated for recent/current climatic conditions, and the accuracy and time homogeneity of the data sets and AOGCM results used in these estimations constitute a large uncertainty.

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Large and irreversible future decline of the Greenland ice-sheet

10.5194/tc-2020-89 ◽

2020 ◽

Author(s):

Jonathan M. Gregory ◽

Steven E. George ◽

Robin S. Smith

Keyword(s):

Climate Change ◽

Steady State ◽

Sea Level ◽

General Circulation ◽

Initial Perturbation ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Circulation Model ◽

Intergovernmental Panel ◽

Recent Climate

Abstract. We have studied the evolution of the Greenland ice-sheet under a range of constant climates typical of those projected for the end of the present century, using a dynamical ice-sheet model (Glimmer) coupled to an atmospheric general circulation model (FAMOUS-ice AGCM). The ice-sheet surface mass balance (SMB) is simulated by the AGCM, including its dependence on altitude within AGCM gridboxes. Over millennia under a warmer climate, the ice-sheet reaches a new steady state, whose mass is correlated with the initial perturbation in SMB, and hence with the magnitude of global climate change imposed. For the largest global warming considered (about +5 K), the contribution to global-mean sea-level rise (GMSLR) is initially 2.7 mm yr−1, and the ice-sheet is eventually practically eliminated (giving over 7 m of GMSLR). For all RCP8.5 climates, final GMSLR exceeds 4 m. If recent climate were maintained, GMSLR would reach 1.5–2.5 m. Contrary to expectation from earlier work, we find no evidence for a threshold warming that divides scenarios in which the ice-sheet suffers little reduction from those which it is mostly lost. This is because the dominant effect is reduction of area, not reduction of surface altitude, and the geographical variation of SMB must be taken into account. The final steady state is achieved by withdrawal from the coast in some places, and a tendency for increasing SMB due to enhancement of cloudiness and snowfall over the remaining ice-sheet, through the effects of topographic change on atmospheric circulation. If late twentieth-century climate is restored, the ice-sheet will not regrow to its present extent, owing to such effects, once its mass has fallen below a threshold of about 4 m of sea-level equivalent. In that case, about 2 m of GMSLR would become irreversible. In order to avoid this outcome, anthropogenic climate change must be reversed before the ice-sheet has declined to the threshold mass, which would be reached in about 600 years at the highest rate of mass-loss within the likely range of the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.

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Estimation of the Greenland ice sheet surface mass balance during 20th and 21st centuries

The Cryosphere Discussions ◽

10.5194/tcd-2-225-2008 ◽

2008 ◽

Vol 2 (2) ◽

pp. 225-254 ◽

Cited By ~ 1

Author(s):

X. Fettweis ◽

E. Hanna ◽

H. Gallée ◽

P. Huybrechts ◽

M. Erpicum

Keyword(s):

Mass Balance ◽

Multiple Regression ◽

21St Century ◽

General Circulation ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

General Circulation Models ◽

Climate Simulation ◽

Surface Mass Balance ◽

Surface Mass

Abstract. Results from a regional climate simulation (1970–2006) over the Greenland ice sheet (GrIS) reveals that more than 97% of the interannual variability of the modelled Surface Mass Balance (SMB) can be explained by the GrIS summer temperature anomaly and the GrIS annual precipitation anomaly. This multiple regression is then used to empirically estimate the GrIS SMB since 1900 from climatological time series. The projected SMB changes in the 21st century are investigated with the set of simulations performed with atmosphere-ocean general circulation models (AOGCMs) of the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4). These estimates show that the high surface mass loss rates of recent years are not unprecedented in the GrIS history of the last hundred years. The minimum SMB rate seems to have occurred earlier in the 1930s. The AOGCMs project that the SMB rate of the 1930s would be common at the end of 2100. The temperature would be higher than in the 1930s but the increase of accumulation in the 21st century would partly offset the acceleration of surface melt due to the temperature increase. However, these assumptions are based on an empirical multiple regression only validated for recent/current climatic conditions, and the accuracy and time homogeneity of the data sets and AOGCM results used in these estimations constitute a large uncertainty.

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Ice-sheet contributions to future sea-level change

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2006.1796 ◽

2006 ◽

Vol 364 (1844) ◽

pp. 1709-1732 ◽

Cited By ~ 143

Author(s):

J.M Gregory ◽

P Huybrechts

Keyword(s):

Mass Balance ◽

Sea Level ◽

General Circulation ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

General Circulation Models ◽

Balance Model ◽

Surface Mass Balance ◽

Surface Mass ◽

Global Average

Accurate simulation of ice-sheet surface mass balance requires higher spatial resolution than is afforded by typical atmosphere–ocean general circulation models (AOGCMs), owing, in particular, to the need to resolve the narrow and steep margins where the majority of precipitation and ablation occurs. We have developed a method for calculating mass-balance changes by combining ice-sheet average time-series from AOGCM projections for future centuries, both with information from high-resolution climate models run for short periods and with a 20 km ice-sheet mass-balance model. Antarctica contributes negatively to sea level on account of increased accumulation, while Greenland contributes positively because ablation increases more rapidly. The uncertainty in the results is about 20% for Antarctica and 35% for Greenland. Changes in ice-sheet topography and dynamics are not included, but we discuss their possible effects. For an annual- and area-average warming exceeding in Greenland and in the global average, the net surface mass balance of the Greenland ice sheet becomes negative, in which case it is likely that the ice sheet would eventually be eliminated, raising global-average sea level by 7 m.

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Elimination of the Greenland Ice Sheet in a High CO2 Climate

Journal of Climate ◽

10.1175/jcli3482.1 ◽

2005 ◽

Vol 18 (17) ◽

pp. 3409-3427 ◽

Cited By ~ 173

Author(s):

J. K. Ridley ◽

P. Huybrechts ◽

J. M. Gregory ◽

J. A. Lowe

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

General Circulation ◽

Climate Changes ◽

Regional Climate ◽

Ice Sheet ◽

Carbon Dioxide Concentration ◽

Greenland Ice Sheet ◽

General Circulation Models ◽

Ice Dynamics

Abstract Projections of future global sea level depend on reliable estimates of changes in the size of polar ice sheets. Calculating this directly from global general circulation models (GCMs) is unreliable because the coarse resolution of 100 km or more is unable to capture narrow ablation zones, and ice dynamics is not usually taken into account in GCMs. To overcome these problems a high-resolution (20 km) dynamic ice sheet model has been coupled to the third Hadley Centre Coupled Ocean–Atmosphere GCM (HadCM3). A novel feature is the use of two-way coupling, so that climate changes in the GCM drive ice mass changes in the ice sheet model that, in turn, can alter the future climate through changes in orography, surface albedo, and freshwater input to the model ocean. At the start of the main experiment the atmospheric carbon dioxide concentration was increased to 4 times the preindustrial level and held constant for 3000 yr. By the end of this period the Greenland ice sheet is almost completely ablated and has made a direct contribution of approximately 7 m to global average sea level, causing a peak rate of sea level rise of 5 mm yr−1 early in the simulation. The effect of ice sheet depletion on global and regional climate has been examined and it was found that apart from the sea level rise, the long-term effect on global climate is small. However, there are some significant regional climate changes that appear to have reduced the rate at which the ice sheet ablates.

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The effect of overshooting 1.5 °C global warming on the mass loss of the Greenland Ice Sheet

10.5194/esd-2017-103 ◽

2017 ◽

Author(s):

Martin Rückamp ◽

Ulrike Falk ◽

Katja Frieler ◽

Stefan Lange ◽

Angelika Humbert

Keyword(s):

Mass Loss ◽

Sea Level Rise ◽

Sea Level ◽

General Circulation ◽

Order Approximation ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

General Circulation Models ◽

Surface Mass ◽

Atmospheric Forcings

Abstract. Sea level rise associated with changing climate is expected to pose a major challenge for societies. Here, we estimate the future contribution of the Greenland ice sheet (GrIS) to sea level change in terms of different ice sheet atmospheric forcings arising from three general circulation models (GCMs), HadGEM2-ES, IPSL-CM5A-LR and MIROC5, for RCP2.6. We run the ice sheet model ISSM with higher order approximation and use a spin-up/inversion scheme to estimate the present day state. The forcing fields for surface mass balance (SMB) and ice surface temperature Ts are computed by the SEMIC model (Krapp et al., 2017) and applied as anomalies to RACMO2.3 fields. According to the three GCMs, warming of 1.5 °C has been reached at GrIS by 2005 (HadGEM2-ES, MIROC5) or as early as 1995 (IPSL-CM5A-LR). Forcing fields suffer from underestimation of polar amplification (MIROC5) and implausible distribution of changes in Ts (IPSL-CM5A-LR). HadGEM2-ES is the most plausible forcing, with globally a peak and decline behaviour leading to overshooting of 1.5 °C and over GrIS a slight recovery of SMB towards values of about half the present day SMB. We find sea level to rise for HadGEM2-ES by 71 mm by 2100 and 189 mm by 2300. Simulated an observed sea level rise 2002–2014 is of the same magnitude, but with a temporal lag to be at least five years (HadGEM2-ES). By end of 22nd century sea level contribution is still 0.46 mm/a for HadGEM2-ES. Hence, even a RCP2.6 peak and decline scenario will lead to significant changes of GrIS including elevation changes up to 100 m and loss of floating tongues. The values of this study may serve as a lower bound, as processes proven to play a major role in GrIS mass loss are not yet represented by the model, but are considerably larger than other studies.

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Large and irreversible future decline of the Greenland ice sheet

The Cryosphere ◽

10.5194/tc-14-4299-2020 ◽

2020 ◽

Vol 14 (12) ◽

pp. 4299-4322

Author(s):

Jonathan M. Gregory ◽

Steven E. George ◽

Robin S. Smith

Keyword(s):

Climate Change ◽

Global Warming ◽

Steady State ◽

Sea Level ◽

General Circulation ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Circulation Model ◽

Intergovernmental Panel ◽

Late 20Th Century

Abstract. We have studied the evolution of the Greenland ice sheet under a range of constant climates typical of those projected for the end of the present century using a dynamical ice sheet model (Glimmer) coupled to an atmosphere general circulation model (FAMOUS–ice AGCM). The ice sheet surface mass balance (SMB) is simulated within the AGCM by a multilayer snow scheme from snowfall and surface energy fluxes, including refreezing and dependence on altitude within AGCM grid boxes. Over millennia under any warmer climate, the ice sheet reaches a new steady state, whose mass is correlated with the magnitude of global climate change imposed. If a climate that gives the recently observed SMB were maintained, global-mean sea level rise (GMSLR) would reach 0.5–2.5 m. For any global warming exceeding 3 K, the contribution to GMSLR exceeds 5 m. For the largest global warming considered (about +5 K), the rate of GMSLR is initially 2.7 mm yr−1, and eventually only a small ice cap endures, resulting in over 7 m of GMSLR. Our analysis gives a qualitatively different impression from previous work in that we do not find a sharp threshold warming that divides scenarios in which the ice sheet suffers little reduction from those in which it is mostly lost. The final steady state is achieved by withdrawal from the coast in some places and a tendency for increasing SMB due to enhancement of cloudiness and snowfall over the remaining ice sheet by the effects of topographic change on atmospheric circulation, outweighing the tendency for decreasing SMB from the reduction in surface altitude. If late 20th-century climate is restored after the ice sheet mass has fallen below a threshold of about 4 m of sea level equivalent, it will not regrow to its present extent because the snowfall in the northern part of the island is reduced once the ice sheet retreats from there. In that case, about 2 m of GMSLR would become irreversible. In order to avoid this outcome, anthropogenic climate change must be reversed before the ice sheet has declined to the threshold mass, which would be reached in about 600 years at the highest rate of mass loss within the likely range of the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.

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Greenland ice sheet contribution to sea level rise during the last interglacial period: a modelling study driven and constrained by ice core data

Climate of the Past ◽

10.5194/cp-9-353-2013 ◽

2013 ◽

Vol 9 (1) ◽

pp. 353-366 ◽

Cited By ~ 42

Author(s):

A. Quiquet ◽

C. Ritz ◽

H. J. Punge ◽

D. Salas y Mélia

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Ice Core ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Interglacial Period ◽

Last Interglacial ◽

Intergovernmental Panel ◽

Orbital Configuration ◽

Global Sea Level

Abstract. As pointed out by the forth assessment report of the Intergovernmental Panel on Climate Change, IPCC-AR4 (Meehl et al., 2007), the contribution of the two major ice sheets, Antarctica and Greenland, to global sea level rise, is a subject of key importance for the scientific community. By the end of the next century, a 3–5 °C warming is expected in Greenland. Similar temperatures in this region were reached during the last interglacial (LIG) period, 130–115 ka BP, due to a change in orbital configuration rather than to an anthropogenic forcing. Ice core evidence suggests that the Greenland ice sheet (GIS) survived this warm period, but great uncertainties remain about the total Greenland ice reduction during the LIG. Here we perform long-term simulations of the GIS using an improved ice sheet model. Both the methodologies chosen to reconstruct palaeoclimate and to calibrate the model are strongly based on proxy data. We suggest a relatively low contribution to LIG sea level rise from Greenland melting, ranging from 0.7 to 1.5 m of sea level equivalent, contrasting with previous studies. Our results suggest an important contribution of the Antarctic ice sheet to the LIG highstand.

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Greenland Ice Sheet Surface Mass-Balance Modeling in a 131-Yr Perspective, 1950–2080

Journal of Hydrometeorology ◽

10.1175/2009jhm1140.1 ◽

2010 ◽

Vol 11 (1) ◽

pp. 3-25 ◽

Cited By ~ 64

Author(s):

Sebastian H. Mernild ◽

Glen E. Liston ◽

Christopher A. Hiemstra ◽

Jens H. Christensen

Keyword(s):

Mass Balance ◽

Sea Level ◽

General Circulation ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Circulation Model ◽

Change Scenario ◽

Surface Mass Balance ◽

Surface Mass ◽

Freshwater Runoff

Abstract Fluctuations in the Greenland ice sheet (GrIS) surface mass balance (SMB) and freshwater influx to the surrounding oceans closely follow climate fluctuations and are of considerable importance to the global eustatic sea level rise. A state-of-the-art snow-evolution modeling system (SnowModel) was used to simulate variations in the GrIS melt extent, surface water balance components, changes in SMB, and freshwater influx to the ocean. The simulations are based on the Intergovernmental Panel on Climate Change scenario A1B modeled by the HIRHAM4 regional climate model (RCM) using boundary conditions from the ECHAM5 atmosphere–ocean general circulation model (AOGCM) from 1950 through 2080. In situ meteorological station [Greenland Climate Network (GC-Net) and World Meteorological Organization (WMO) Danish Meteorological Institute (DMI)] observations from inside and outside the GrIS were used to validate and correct RCM output data before they were used as input for SnowModel. Satellite observations and independent SMB studies were used to validate the SnowModel output and confirm the model’s robustness. The authors simulated an ∼90% increase in end-of-summer surface melt extent (0.483 × 106 km2) from 1950 to 2080 and a melt index (above 2000-m elevation) increase of 138% (1.96 × 106 km2 × days). The greatest difference in melt extent occurred in the southern part of the GrIS, and the greatest changes in the number of melt days were seen in the eastern part of the GrIS (∼50%–70%) and were lowest in the west (∼20%–30%). The rate of SMB loss, largely tied to changes in ablation processes, leads to an enhanced average loss of 331 km3 from 1950 to 2080 and an average SMB level of −99 km3 for the period 2070–80. GrIS surface freshwater runoff yielded a eustatic rise in sea level from 0.8 ± 0.1 (1950–59) to 1.9 ± 0.1 mm (2070–80) sea level equivalent (SLE) yr−1. The accumulated GrIS freshwater runoff contribution from surface melting equaled 160-mm SLE from 1950 through 2080.

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